High-resolution andin-situtransmission electron microscopy investigation of the martensitic fcc ↔ dhcp phase transformations in Co-Fe single crystals

Abstract

Abstract The thermally induced fcc↔dhcp martensitic phase transformations were studied in a Co-5.75 at.% Fe single crystal. Transmission electron microscopy (TEM) methods were applied including in-situ experiments; lattice fringe and high-resolution transmission electron microscopy (HRTEM) images were analysed. At room temperature the as-grown single crystal was in the dhcp low-temperature phase and dhcp lamellae with an average thickness of 10–11nm were observed that are separated by very thin fcc lamellae of retained austenite. The shape of the transformation fronts and the lack of long-range strains indicate that the Shockley Burgers vectors of the partial dislocations occurring at the fronts are compensating each other to a large extent. The reverse dhcph →fcc transformation was studied during in-situ heating. HRTEM images were used to analyse the partials located at the fronts of the transformation by drawing Burgers circuits around them. In a HRTEM image (with a [1210]dhcp ≡ [110]fcc beam direction)...